The present invention relates to mechanically variable resistance elements having elements thereof applied to a base.
The use of printed circuitry, and particularly thick film techniques, in electronic circuitry permits a substantial reduction in their size. However, certain electronic components, including rheostats or potentiometers cannot be produced by such techniques. There has thus arisen a need for elements of this type which may be contructed on a scale commensurate with that of the miniaturized thick film circuitry.
It is, therefore, the object of the present invention to provide a variable resistance device which, while not so limited, finds particular utility in miniaturized thick film circuitry, as by utilizing elements integrally formed in such circuitry. The device of the present invention is small in size, simple in construction and easy to disassemble for inspection or other purposes.
The variable resistance device of the present invention includes a thick film electrical conductor affixed to the underside of a supporting substrate and extending around a hole in the substrate. A resistor element, which may also be film-like, is affixed to the underside of the substrate radially spaced from the conductor. A knob has a disc bearing on the top side of the substrate and a cylinder containing a slot or other tool responsive configuration by which the knob may be rotated. A pair of projections depend from the bottom of the disc and extend through and beyond the hole. The projections may comprise chord-like portions of the cylindrical form of the hole. A carrier plate is mounted on the lower ends of the projections adjacent the underside of the substrate. The carrier is rotatable with the knob.
A wiper, typically having a plurality of brushes, is mounted on the upper surface of the carrier to engage and electrically connect the conductor and resistor element. The wiper is positioned along the resistance element by rotation of the knob to establish the resistance of the device. The projections may be bent inwardly to remove the carrier, affording rapid and easy inspection, replacement of parts and dismantling of the device. The device may be covered by a casing on the top side of the substrate through which the slot containing cylinder extends. A cover on the underside of the substrate protects the plate, wiper, conductor and resistor element.